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Check out this simple opamp circuit It is a wrongly wired inverting amplifier circuit. In fact, the feedback provided is positive instead of the desired negative feedback.

But, circuitlab's transient simulation incorrectly gives the same results irrespective of the signs on the input terminals of the opamp. A conventional spice simulation of the circuit would show the output saturated at either the plus or the minus power supply rail.

Thank you @signality for the very insightful reply and also for the good links. I now agree that the CL simulation result was correct.

The calculations show that given a large enough open loop gain, the inverting amplifier circuit has a closed loop gain of -1 (assuming R1=R2). Importantly, this is true irrespective of whether the feedback is positive or negative.

Hence, one would expect identical outputs from both the circuits (inverting amplifiers with rail-less opamp models). In fact, for the rail-less opamp models used, this is exactly what we get. (Yes, I completely agree - CL was correct!)

Now lets look at inverting amplifiers with supply rails considered. Am interested in understanding why the output waveforms differ between the positive and the negative feedback cases? For example, the negative feedback circuit seems to be following the ideal output within swing limits, while the positive feedback circuit doesn't do that.

On the other hand, if the supply rails are increased to avoid clipping, we get identical waveforms ! However, this is expected.